The overall goal of this research is to develop a clinically useful way to enhance the penetration and effectiveness of photosensitizers (PS) in human Dental plaque for prevention and treatment of periodontitis. The hypotheses to be tested are: (a) Laser-generated photomechanical waves (PW) can induce in vitro enhanced permeabilization of oral bacterial biofilms of different density to positively charged PS, such as a polycationic conjugate between poly-L-lysine (p1) and the PS chlorin e6 (ce6) and the cationic methylene blue (MB), an approach which can significantly increase uptake of ce6 and MB by bacteria, and (b) Photodestruction of these bacterial biofilms in vitro may be possible after their sensitization with the pl-ce6 conjugate and MB followed by exposure to PW and red light. The interaction of the PS with biofilms of periodontopathogens will be studied using two in vitro models: a) monospecific biofilms growing attached to natural enamel surfaces, and b) multispecific biofilms growing on natural enamel surfaces in a chemostat system. The uptake of PS will be quantitated by measuring fluorescence and their local interaction with bacteria and the biofilm matrix will be evaluated by confocal scanning laser microscopy. Laser-induced PW will be applied in the presence of the PS to disorganize the biofilm structure and increase their penetration. Other disorganizing agents of the bacterial biofilm will be used for comparisons. In all cases, the penetration of the PS will be evaluated by confocal scanning laser microscopy. In the same biofilm models the photodynamic effects of the PS will be established and PW-enhanced photosensitization of periodontopathogens by the PS will be evaluated.